Ion implantation is a common process during semiconductor fabrication. For example, ions of boron, arsenic, phosphorous, antimony, aluminum and gallium may be implanted in silicon, germanium or other type IV semiconductor material to change the number of negative or positive charge carriers.
A typical conventional ion implanter device has a beam sized so as to expose an entire surface of a wafer simultaneously, such as a 150 mm wafer. In order to reduce product costs, semiconductor foundries have moved towards using larger wafers. For example, technology for fabricating integrated circuits on 450 mm wafers is actively being developed. As wafer size increases, it becomes more difficult to provide an ion beam of uniform intensity and sufficiently large diameter to expose an entire wafer surface simultaneously.
Another type of ion implanter, such as the “iPulsar” system sold by Advanced Ion Beam Technologies, Inc. of San Jose, Calif., has a beam that is smaller than the larger sized wafers. The system has a wafer manipulator 100 capable of moving the wafer past the beam to expose the surface sequentially.
FIGS. 1 and 2 are schematic diagrams of the wafer of the iPulsar type system.
The system 100 has a fixed-location beam 110. The wafer 130 is mounted at the end of a scanner arm 120. The scanner arm 120 has two types of motion. As shown in FIG. 1, the scanner arm 120 pivots about a pivot axis located at a point px, py, with a pivot angle theta (θ). The wafer 130 and pivot arm 120 are also shown in phantom at different positions to represent examples of different angles θ through which the scanner arm 120 pivots.
FIG. 2 shows that the wafer manipulator 100 has a means (shown by actuator 140) for raising and lowering the pivot axis px, py of the scanner arm 120. When the pivot axis px, py is raised up, the lower portion of the wafer 130 (closer to the pivot axis) is exposed to the beam 110. When the pivot axis px, py is lowered, the upper portion of the wafer 130 (farther from the pivot axis) is exposed to the beam 110.
One of ordinary skill in the art can appreciate that the scanner type ion implanter can be used for implanting a variety of wafer sizes, including wafers larger than the beam. Because the wafer size is not limited by the beam size, a relatively smaller beam having good uniformity can be used.
Improved methods of ion implantation using a scanner type implanter are desired.